Today the first Store update for the
8.1 Developer Preview Music App went live in the Store. Users once they
update their Music App from the store will start to get version 2.5.2842 .
This is part of the continuous releases you can expect with the WP8.1 Music
client for the coming year.

In release v2.5.2842 you
will find:

Numerous stability fixes, including many of the
reported black screens

Full Cortana integration including playing
Playlists by name

UI Polish to improve animations and transitions
between UI views

Improved messaging for encountered errors, such
as unplayable content in collections

Some of what is targeted for the series of coming
releases:

Continued focus on Stability and Performance
improvements

Background initial sync of local and cloud
content (Note: This had been targeted for the last store update, but we
pushed it out one more release to do some additional testing)

Fast Forward/Rewind by sliding progress bar in a
song

UX layouts on buttons and metadata in now
playing to better utilize space and make for better interaction

Support for large play queue(including playlist)
greater than 100 songs

The next Store release of the Music App is coming within the
next 2 weeks. We will continue to update this site with coming features
and releases, and if you haven’t, be sure to visit http://xboxmusic.uservoice.com/ and enter and vote for the features you want to see next.